1. Field of the Invention
The present invention relates to a method for driving a fuel injection pump which is used to supply fuel to an internal combustion engine (hereafter referred to simply as an “engine”), and more particularly relates to a method for driving a fuel injection pump used in engines that are mounted on two-wheeled vehicles or the like.
2. Description of the Related Art
For example, as is described in Japanese Patent Application Laid-Open No. 2001-221137, a fuel injection pump in which fuel conducted from a fuel tank by means of a feed pipe is pressure-fed by means of an electromagnetically driven plunger pump, fuel in the initial region of the pressure-feeding stroke is circulated back to the fuel tank by means of a return pipe, and fuel in the later region of the pressure-feeding stroke is injected into the intake passage from an injection nozzle, is known as a fuel injection pump used in engines mounted on two-wheeled vehicles or the like.
In this apparatus, a discharge mechanism is provided which circulates fuel containing vapor (air bubbles) back to the fuel tank via the return pipe in advance, before the fuel that has been pressure-fed by the plunger pump is injected by the injection nozzle.
In the abovementioned apparatus, there may be cases in which large quantities of vapor are generated in the supplied fuel when the ambient temperature is high, or as a result of heat generated by the coil during electromagnetic driving or the like; accordingly, it is necessary to remove this generated vapor with good efficiency.
For example, the temperature is high immediately after the engine has been stopped or the like; as a result, there is a danger that large quantities of vapor will be generated. Accordingly, in cases where the engine is re-started from this high-temperature state, it is difficult to re-start the engine (good re-starting characteristics are not obtained); furthermore, a certain amount of time is required in order to discharge the generated vapor by means of the discharge mechanism, so that stable fuel injection cannot be obtained.
Furthermore, in cases where the engine is placed in an idle operating state following high-load operation, the amount of fuel circulation (recycling) is small while the environment is a high-temperature environment; as a result, the vapor that is generated cannot be reliably discharged.